The transition marked the Macintosh platform's second migration to a new CPU architecture. The first was the switch from the Motorola 68000 ("68k") series architecture (used since the original Macintosh 128K) to the PowerPC architecture. Apple is the only personal computer company to have successfully completed such a transition – competitors Commodore and Atari never regained their market positions after their switch from 6502 to 68k in the mid-1980s[2][3] and stopped manufacturing computers in the early 1990s, around the time Apple was switching to PowerPC.

Apple's initial press release indicated the transition would begin by June 2006, and finish by the end of 2007, but it actually proceeded much more quickly. The first generation Intel-based Macintoshes were released in January 2006 with Mac OS X 10.4.4 Tiger, and Steve Jobs announced the last models to switch in August 2006, with the Mac Pro available immediately and with the Intel Xserve available by October 2006.[4] The Xserve servers were available in December 2006.[5]

Apple released Mac OS X v10.6 "Snow Leopard" on August 28, 2009 as Intel-only, removing support for the PowerPC architecture. It is also the last Mac OS X version that support PowerPC based applications.[6]

January 10, 2006: Jobs announces the first two computers in this series, the 15" MacBook Pro and iMac Core Duo line, both using an Intel Core Duo chip and offers to trade in the Developer Transition Kits for iMacs.

February 28, 2006: Jobs announces that the Mac mini now also comes with an Intel Core chip, in either the Solo or Duo varieties.

April 5, 2006: Apple announced the release of Boot Camp, which allowed users of Intel-based Macs to run Windows XP[8] (and later versions of Boot Camp allow later versions of Windows).

October 26, 2007: Apple ships Mac OS X 10.5 "Leopard", the final release with PowerPC support. Macs using a G3 processor cannot boot this operating system, as only G4 and G5 processors with a minimum 867 MHz clock speed are supported.

August 28, 2009: Apple ships Mac OS X 10.6 "Snow Leopard" exclusively for Intel Macs. PowerPC Macs cannot boot this OS. This is also the final release with Rosetta, allowing PowerPC software to run on an Intel Mac.

March 1, 2011: The beta version of the then-upcoming Mac OS X Lion drops "Rosetta" and will not be able to run PowerPC based software.[10]

The names of some of Apple's desktop and laptop product lines changed between the PowerPC version and the corresponding Intel version. Most notably, the word "Power" was dropped from all product lines. During the Keynote address at Macworld in 2006, where the first Intel-based Macs, the iMac and MacBook Pro, were announced, Steve Jobs remarked that the new naming schemes for their products reflected their desire to have "Mac" in the name of all of their computers, and because they were "done with power." This was in reference to the fact that the previous PowerPC G5 processors were not energy efficient, and therefore used far too much power to be used in any portable Macs.

The first known attempt to move to Intel platforms was the Star Trek project from spring 1992 to 1993, a joint effort with Novell to port Mac OS to run on ordinary 486 PCs. It was based on Novell's next in-development version of DR DOS with its pre-emptive multitasker, which provided a hybrid 32-bit/16-bit core system similar in architecture to Windows 3.1 in 386 Enhanced Mode, but without a GUI. The ported System 7.1 ran on top of this environment. While the project was successful with running pre-beta versions it was stopped in 1993 after management and strategy changes. The core system (but without the Star Trek-specific components) was later released as part of Novell DOS 7.

The Macintosh line underwent a similar transition between 1994 and about 1996, when Apple switched from Motorola's 68k series of chips to IBM/Motorola PowerPC processors, developed jointly by Motorola, Apple, and IBM. This took several years, during which Apple produced versions of the classic Mac OS that could run on either platform, introduced fairly low-level emulation of the 68k architecture by the PowerPC models, and encouraged third-party developers to release fat binaries that could run natively on either architecture.

Apple later transitioned the Macintosh from the earlier classic Mac OS to Mac OS X. This transition also took a number of years, and was facilitated by the inclusion of Classic, an environment in which an instance of Mac OS 9 could be run, permitting the execution of programs that had not been ported to Mac OS X, as well as the introduction of Carbon for Mac OS 9 and Mac OS X, allowing programs to run natively on either system.

Jobs revealed at the 2005 WWDC, that every version of Mac OS X had been secretly developed and compiled for Intel processors (as well as PowerPC) as they were developed; the portability of its predecessor NeXTSTEP had been maintained. It is not publicly known whether Apple maintains current builds for any other architectures although the related iOS runs on the iPhone's ARM architecture.

Steve Jobs stated that Apple's primary motivation for the transition was their disappointment with the progress of IBM's development of PowerPC technology, and their greater faith in Intel to meet Apple's needs. In particular, he cited the performance per watt projections in the roadmap provided by Intel.[12] This is an especially important consideration in laptop design, which affects the hours of use per battery charge.

In June 2003, Jobs had introduced Macs based on the PowerPC G5 processor and promised that within a year, the clock speed of the part would be up to 3 GHz. Two years later, 3 GHz G5s were still not available, and rumors continued that IBM's low yields on the POWER4-derived chip were to blame. Further, the heat produced by the chip proved an obstacle to deploying it in a laptop computer, which had become the fastest growing segment of the personal computer industry.

Some observers were surprised that Apple had not made a deal with AMD, which had in recent years become a strong competitor to Intel. AMD had recently released its competitive 64-bit Opteron platform,[13][14] and by moving straight to x86-64 Apple would have had one less architecture transition. Analysts have speculated that AMD's lack of low-power designs at the time were behind the decision to go with Intel.[12] However, in 2011, Apple investigated using AMD’s low power Llano APU for the MacBook Air, but eventually opted for Intel due to AMD's potential inability to supply enough Llano processors to meet demand.[15]

Advocates of the transition pointed out the potential for the new Intel Mac systems to run four classes of software at native speeds: Mac OS X binaries, Java/.NET applications, Unix applications, and Win32/x86 applications.

Originally, emulation software such as DOSBox or Microsoft Virtual PC was required to run x86 software on the Macintosh. Such software could now enjoy much more success with near-native performance through virtualization, such as is currently being done by Parallels Desktop for Mac and VMware Fusion. For those customers wishing to achieve a more conventional environment, a dual boot solution is possible on an x86 Apple device using Boot Camp software (which includes Windows drivers for Mac hardware). Some third-party partitioning options can even provide triple, or even quadruple boot.

Although most games depend on the use of DirectXAPIs not available on Mac OS X (on either processor type), it should be easier to port OS-independent code, such as OpenGL, now that developers no longer have to resolve endian, and other ISA dependency issues associated with moving from x86 to PowerPC.

The announcement of Apple's intention to switch to Intel-based Macs caused concern because Rosetta, the PowerPC dynamic translator, when first announced, emulated a G3 at only 60-80% of a similarly powered CPU's clock speed. Apart from this, Classic, the Mac OS 9 virtualization for Mac OS X, was not ported to the x86 architecture, leaving the new Intel-powered Macs incompatible with original Mac OS applications without a proper third-party PowerPC emulator.

The performance of Intel's chipsets was a concern, along with the x86 architecture itself, and whether it would affect system performance and application quality. Other problems include endianness and reduced floating point performance in real world applications relative to equivalent or contemporary PowerPC processors.

It was also feared that it may be possible for Windows and Windows applications to run natively on Mac hardware, possibly killing off Mac OS X and/or applications developed for it. There was concern that the early announcement of the change would cause an Osborne effect, and there was the possibility that Intel could force Apple to use the Intel Inside branding. In addition, Apple had nurtured a feeling of animosity toward Intel among its loyal base. It would take time and money to convince Apple's most loyal customers that Intel was acceptable.

There were also fears that Intel, which took part in the development and implementation of the USB, would force Apple to drop all development and support of its FireWire serial bus on all Intel Macs. This did not occur, as FireWire ports continued to be included on all Macs, except certain notebook configurations beginning with the MacBook Air in 2008, until being replaced by the faster Thunderbolt port.

Many of these fears were put to rest at Macworld 2006 with the arrival of the first Intel-based Macs. Rosetta was improved to offer much faster speeds than originally demonstrated (though benchmarks suggest that PowerPC code still does not perform as well under emulation on a Core Duo iMac as it does on a G5 iMac[16]). Intel's Core Duo CPUs perform nearly as well as the most powerful Power Mac G5 towers.

Applications native to both PPC and Intel-based Macs such as Safari web browser were found to perform better on the Intel-based Mac than on the PPC-based Mac. However, classic Mac OS applications will not run directly on Intel Macs. Pre-Mac OS X applications can only be run on Intel Macs by using emulators such as vMac, Basilisk II, and SheepShaver, though the lack of stability of these emulators severely limits their functionality.

Fears of an Osborne effect were dismissed after sales of Macs for the Christmas 2005 quarter saw an increase over the previous Christmas. Unlike Windows-based PC counterparts "Intel Inside" stickers have never been included on any Apple product.[17]

There were questions over the extent to which Apple would retain control over the non-processor components of the system design. Apple is traditionally a systems builder, and some feared that Apple's industrial design philosophy may be affected if the company switched to commodity parts. Others noted that Apple has slowly been switching to standard parts since the introduction of the PCI Power Mac in 1995, and said that using a non-Apple chipset in itself would not harm the Mac's image.

The use of the x86 architecture allows Windows to run natively on Apple hardware, and opens the possibility of using the Wine package to run Windows executables directly. Some[who?] fear that the change will make Mac OS X a less valuable target for software developers, since Mac OS X users can use a dual-boot setup or a Wine variant (such as CrossOver Mac or Darwine) to run Windows apps instead. Others say that it could be a boon to switchers, since they would not have to leave their Windows applications behind while trying out Mac OS X. The idea of Mac OS X being available on regular PCs has also been discussed, but Apple has said that they will not allow regular PCs to run Mac OS X.[19] The OSx86 Project, however, is able to install Mac OS X on non-Apple PCs. It was previously thought that since Windows XP is incompatible with the Extensible Firmware Interface, it would not be run on Intel-based Macs.[20] Prior to the Boot Camp announcement, a prize contest[21] resulted in a working solution for dual-booting Windows XP and Mac OS X on an Intel Mac. Microsoft has announced that Windows Vista will not be EFI-compatible on 32-bit platforms, but the later versions of Boot Camp allow Vista to be installed on any Intel Mac.

Intel was seen among the Mac community as a purveyor of hot-running chips (especially the Pentium 4). Apple themselves mocked the Pentium range in their "Toasted Bunnies" advertisements of the late 1990s. However, the Pentium M chips, which were designed for laptop use, run much cooler than the Pentium 4. Apple claimed the then-new Intel Core chips, which are based on the Pentium M microarchitecture, would have dramatically better performance per watt than the PowerPC G4 and G5.

Finally, the relative quality of the x86 architecture has been discussed. Critics of the switch say that x86 was a poor choice because of its lack of hardware registers compared to the PowerPC, and the lack of AltiVec (also known as Velocity Engine). Proponents have responded by saying that the x86 architecture has evolved greatly since the original 8086 was introduced, and that CPUs in general have combined RISC and CISC philosophies in their internal designs for some time, making the distinction obsolete. They also point out that improved SSE could equal AltiVec, and that most programmers rarely deal with x86's peculiarities because the compiler does the work.

The PowerPC G5 was a 64-bit design, although very few applications made use of the increased address space. In contrast the original Core Solo and Core Duo chips were 32-bit. On August 7, 2006, Apple released the Mac Pro and Intel-based Xserve, introducing Intel 64 (Intel's implementation of x86-64) architecture into the lineup through the use of the Xeon processor. As of August 7, 2007, all other computers in Apple's product line have been updated with the 64-bit Core 2 Duo.

While the current benchmarks comparing Core Duo to Core 2 Duo processors show very little difference when running in 32 bit, the 64 bit edge has become more of an issue with the release of Mac OS X v10.6 (Snow Leopard), and now users can dual boot Windows 7 in full 64-bit mode.

Java applications (that do not rely on Java Native Interface), some DashboardWidgets, and scripts that execute inside an interpreter all work immediately on both processors and are immune to changes. Mac OS X applications that cannot be migrated run inside a PowerPC dynamic translator on Intel called "Rosetta." Rosetta was originally limited to a G3 instruction set, but currently supports AltiVec and the G4 instruction set, leaving only the G5 additions unsupported. Rosetta is an instruction translator comparable to the 68k emulator that allows PowerPC Macintoshes to run pre-PowerPC code, rather than a virtual system like Classic; it does not require a second operating system to be loaded as a subsystem before the application can work.

AltiVec itself has been encapsulated since Mac OS 10.3 by a vectorization library; this library uses AltiVec on the PowerPC and SSE (or equivalent regular instructions) on x86.

A new version of Xcode was released that supported the generation of Universal Binaries for Intel and PowerPC, the new system's equivalent of the earlier 68k-PowerPC fat binaries. Cocoa applications can be ported simply by recompiling them and checking for endianness problems. Carbon applications required some additional tuning, but not of the complexity of the transition from Mac OS 9. Applications written using MetrowerksCodeWarrior suite had to be modified; those that use PowerPlant required further code changes, described by Apple and Metrowerks.

Classic is not supported on the x86 architecture. This means that pre-Mac OS X software does not run on Mac OS X out of the box, to which some users running older applications (such as QuarkXPress 4 and 5) objected.[citation needed] However, third-party emulators, such as Mini vMac, Basilisk II, and SheepShaver, have been ported to Intel-based Macs, allowing some pre-Mac OS X software to run.